Power Control. Establishing specific power settings is accomplished
through collective pitch adjustments-RPM is controlled automatically in
a turbine engine helicopter. Once a desired power setting is established,
frequent attention to the torque meter is necessary. At any given airspeed,
a specific power setting determines whether the helicopter is in level
flight, in a climb, or in a descent. For example, cruising airspeed maintained
with cruising power will result in level flight. If you increase the power
setting and hold the airspeed constant, the helicopter will climb. Conversely,
if you decrease power and hold the airspeed constant, the helicopter will
descend. As a rule of thumb, in a turbine engine helicopter a 10 percent
change in the torque value required to maintain level fright will result
in a climb or descent of approximately 500 feet per minute, if the airspeed
remains the same.

If the altitude is held constant, power determines the airspeed.
For example, at a constant altitude, cruising power results in cruising
airspeed. Any deviation from the cruising power setting results in a change
of airspeed. When power is added to increase airspeed, the nose of the
helicopter pitches up and yaws to the right; when power is reduced to decrease
airspeed, the nose pitches down and yaws to the left. The yawing effect
is most pronounced in single-rotor helicopters, and is absent in helicopters
with counter rotating rotors. To counteract the yawing tendency of the
helicopter, apply pedal trim during power changes.

To maintain a constant altitude and airspeed in level flight,
coordinate pitch attitude and power control. The relationship between altitude
and airspeed determines the need for a change in power and/or pitch attitude.
If the altitude is constant and the airspeed is high or low, change the
power to obtain the desired airspeed. During the change in power, make
an accurate interpretation of the altimeter; then counteract any deviation
from the desired altitude by an appropriate change of pitch attitude. If
the altitude is low and the airspeed is high, or vice versa, a change in
pitch attitude alone may return the helicopter to the proper altitude and
airspeed. If both airspeed and altitude are low, or if both are high, a
change in both power and pitch attitude is necessary.

To make power control easy when changing airspeed, it is necessary
to know the approximate power settings for the various airspeeds which
will be flown. When the airspeed is to be changed any appreciable amount,
adjust the power so that the torque is approximately 5 percent over or
under that setting necessary to maintain the new airspeed. As the power
approaches the desired setting, include the torque meter in the cross-check
to determine when the proper adjustment has been accomplished. As the airspeed
is changing, adjust the pitch attitude to maintain a constant altitude.
A constant heading should be maintained throughout the change. As the desired
airspeed is approached, adjust power to the new cruising power setting
and further adjust pitch attitude to maintain altitude. Overpowering and
underpowering torque approximately 5 percent is the normal procedure. This
results in a change of airspeed at a moderate rate, which allows ample
time to adjust pitch and bank smoothly. The instrument indications for
straight-and-level flight at normal cruise, and during the transition from
normal cruise to slow cruise, are illustrated in Figures 6-6 and 6-7. After
the airspeed has stabilized at slow cruise, the attitude indicator will
show an approximate level pitch attitude.

The altimeter is the primary pitch instrument during level flight,
whether flying at a constant airspeed, or during a change in airspeed.
Altitude should not change during airspeed transitions. The heading indicator
remains the primary bank instrument. Whenever the airspeed is changed any
appreciable amount, the torque meter is momentarily the primary instrument
for power control, and it should be adjusted to indicate an exact power
setting. When the airspeed approaches that desired, the airspeed indicator
again becomes the primary instrument for power control.

Figure 6-6. Straight-and-level flight (normal cruising airspeed).

Figure 6-7. Straight-and-level flight (airspeed decreasing).

The cross-check of the pitch and the bank instruments to produce
straight-and-level flight should be combined with the power control instruments.
With a constant power setting, a normal cross-check should be satisfactory.
When changing power, however, the speed of the cross-check must be increased
to cover the pitch and bank instruments adequately. This is necessary to
counteract any deviations immediately.